Wave transmission network



March 1947- T. R. FINC IH ET AL 2,416,683

WAVE TRANSMISSION NETWORK Filed Oct. 26, 1944 FIGS).

TRF/NCH 7 MENTOR 'DAMCLEAN BY: M DTT T T T /FWJW A T TOR/VEV Patented Mar. 4, 1947 WAVE TRANSMISSION NETWORK Tudor It. Finch, Jackson Heights, N. Y., and David A. McLean, Chatham, N. J., assignors t Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 26, 1944, Serial No. 560,508

20 Claims.

This invention relates to wave transmission networks and more particularly to those of the type comprising series inductance and shunt capacitance.

Objects of the invention are to reduce the size, weight and cost of such networks, to simplify their construction and assembly, and to improve their stability.

The network in accordance with the invention comprises a form, made of insulating material, upon which is wound insulated wire to provide an inductor. The winding may be continuous or it may consist of a number of series-connected sections longitudinally spaced along the form. Over the winding is applied one or more coats of organic insulating enamel. Over this insulating layer is applied an adherent, conducting coating which extends only part way around the form. If the inductor is a continuous winding the conducting coating may be of uniform width for the entire length of the winding, or it may be divided into a number of longitudinally spaced sections, connected by a narrow strip of conducting coating. If the inductor is wound in sections the conducting coating may be applied only over the inductor sections. There is thus formed one or more capacitors the inner electrode of which is the coil winding, the dielectric of which is the insulation on the wire and the layer of organic insulating enamel, and the outer electrode of which isthe conducting coating. The enamel performs a threefold function: it serves to hold the winding in place, increases the voltage rating of the capacitor, and firmly binds the outer electrode to the dielectric.

The electrical circuit of the network is of the ladder type, comprising series lnductances and shunt capacitances. By properly evaluating these inductances and capacitances the network may, for example, be designed to provide a phase characteristic which is substantially linear with frequency.

Since the network is simple to construct and assemble, its cost is comparatively low. It is also small in size, light in weight, and very stable with respect to changes in temperature or humidity, or with exposure to vibration. These latter qualities are of special importance in air-borne equipment.

The nature of the invention will be more fully understood from the following detailed description and by reference to the accompanying drawings, in which like reference characters refer to similar or corresponding parts and in which:

Figs. 1, 2, and 3 are, respectively, a top, bottom and side view of a network in accordance with the invention having lumped inductance and lumped capacitance;

Fig. 4 is a diagrammatic cross-section through an inductor section;

Fig. 5 is a side view of a modified form of the network, with continuous inductance and lumped capacitance;

Fig. 6 is a side view of another modification having continuous inductance and continuous capacitance; and

Fig. 7 gives the schematic circuit of the network.

As shown in Figs. 1, 2, 3 and 4 one'embodiment of the network in accordance with the invention comprises a form I upon which is wound a wire 2 to provide an inductor. The form I is tubular and is made of suitable insulating material such, for example, as phenol fiber. The wire 2 has an insulating covering such, for example, as enamel, and is so wound as to provide a number of inductor sections 3 spaced apart along the length of the form I by the distance D. The spacing pins 4 serve to locate the inductor sec tions 3 in their proper positions. The wire 2 is anchored at its ends to the terminal pins 6 and 1, respectively. The form I, with the inductor sections 3 in place, may now be baked for several hours at a temperature of, say, degrees centigrade and allowed to cool to room temperature in a desiccator.

The entire structure is now given one or more coats of enamel 8 such, for example, as a suitable resinous or polymeric material or thermosetting organic material dissolved in a volatile solvent.

The coats may conveniently be applied by dipping. After each coat the structure is held in a vertical position and subjected to a curing cycle, to drive off the volatile solvent. Further curing above room temperature is then required to complete the cure of the film, the exact treatment depending upon the nature of the insulating material being applied and the volatility of the solvent. For each consecutive coat the form I is inverted for dipping and curing as an aid in obtaining a uniform coat. The number of coats to be applied depends primarily upon the capacitance and the dielectric strength required.

Over each inductor section 3 and the layer of enamel 8 is applied an adherent, conducting coating 9. This extends only part way around the form I in order to avoid forming a shortcircuited turn which would afiect the value of the inductance and introduce considerable un desired dissipation. The coating 9 may-conveniently be applied as a metallic spray or paint comprising, for example, finely divided silver powder, a synthetic resin, and an organic solvent for the resin. After application the coating is air dried or mildly heated to drive off the solvent, leaving an adherent, conducting coating of silver and solidified resin. If the coating 9 is applied as a spray, the portions of the form I not to be coated may be covered with adhesive tape, which is later removed.

The diagrammatic cross-section of Fig. 4 through an inductor section 3 shows the relationship between the various component parts. The conducting coating 9 forms one electrode of a capacitor the other electrode of which is con-' stituted by the winding of the inductor section 3. The insulation on the wire 2 and the layer of organic insulating enamel 8 constitute the dielectric. The layer 8, in addition to serving as a dielectric, holds the'winding 3 in place and forms a firm bond with the plating ,9, thus contributing materially to they stability of the network when exposed to vibration or to changes in temperature or humidity.

It is preferable at first to make the electrodes 9 somewhat smaller than required to provide the desired capacitance C. Each capacitance C may then be measured and the electrodes 9 individually enlarged in area sufiiciently to give the proper value of C. The electrodes 9 may conveniently be extended by painting on silver paste with a small brush. After each electrode 9 has been built out to the required area they are all electrically connectedtogether by a strip of conducting coating l l which terminates in the rings of conducting coating 82 around the ends of the form I. In order to facilitate the making of soldered connections, the rings l2 are, in turn, encircled. by bands of metal 43, M having at their ends a pair of flanges l6 which may be spot-welded asshown at I 1. The holes l3 through the flanges l6 are provided'to accommodate the connecting wires.

As shown by the schematic circuit of Fig. 7 the network is of the ladder type, comprising a number of series-connected inductor sections 3 and shunt capacitances C connected between a pair of input terminals ii, 13 and a pair of out-put terminals i, M. By proper choices of the inductances, of the sections 3, the spacing D between sections, and the capacitances C the network may be designed as a delay network having a substantially linear phase-frequency characteristic. The over-all phase shift will depend upon the number of sections. In Figs. 1 and 2 the central portion ofthe network has been removed and in Fig. 3 only the end portion is shown, in order to save drawing space. In Fig. ,7 the missing portion is indicated by the dashed lines. Of course, any required number of sectionsmay be provided in a single network. 'Als,o,-the network may be designed to have other types oftransmission characteristicaxi-f desired.

Fig. 5 shows a side view of theend portion of a modified form of the network which is similar to I tion, similar to the network of Fig. 5 except that the electrodes 9 have been shortened and the connecting strip ll widened to provide a single continuous electrode 2! of uniform width extending substantially from one end of the inductor I9 to the other. This form is even cheaper to construct, since the separate electrodes 9 have been eliminated. The modified structures of Figs. 5 and 6 may be designed to have substantially the same transmission characteristics as the network shown in Figs. 1, 2, 3 and 4.

What is claimed is:

1. A wave transmission network comprising a form made of insulating material, an inductor wound on said form, a layer of organic insulating enamel over said inductor, and an adherent, conducting coating applied over said enamel and firmly bonded thereto, said inductor being a continuous, closely spaced winding extending substantially from one end of said form to'the other and said conducting coating extending in uniform width substantially from one end of said inductor to the other and part way only around said inductor.

2. A network in accordance with claim 1 in which said enamel comprises a suitable resinous material and a volatile solvent.

3. A network in accordance with claim 1 in which said enamel comprises a suitable polymeric material and a volatile solvent.

4. A network in accordance with claim 1 in which the area of said conducting coating is proportioned with respect to the inductance of said inductor to provide a phase shift which is substantially linear with frequency.

5. A network in accordance with claim 1 in which said conducting coating comprises silver.

6. A network in accordance with claim 1 in which said conducting coating comprises a mixture of silver powder, a synthetic resin, and an organic solvent for the resin.

7. A network in accordance with claim 1 in which said enamel comprises a suitable resinous material and a volatile solvent and said conducting coating comprises a mixture of silver powder, a synthetic resin, and an organic solvent for the resin.

8. A network in accordance with claim 1 in which said enamel comprises a suitable polymeric material and a volatile solvent and said conducting coating comprises a mixture of silver powder, a synthetic resin, and an organic solvent for the resin. 1

9. A network in accordance with claim 1 in which said inductor comprises wire having an insulating covering. a

10. A network in accordance with claim -1 in which said inductor comprises wire having an enamel coating. p

1.1. A wave transmission network comprising a form made of insulating material, an inductor wound on said form, a layer of organic insulating enamel over said inductor, and an adherent, conducting coating applied over .saidenamel and firmly-bonded thereto, said inductor being a continuous, closely spaced winding extending substantially from one endof said form to the other and said conducting coating comprising a plu- 13. A network in accordance with claim 11 in which said enamel comprises a suitable resinous material and a volatile solvent.

14. A network in accordance with claim 11 in which said enamel comprises a suitable polymeric material and a volatile solvent.

15. A network in accordance with claim 11 in which said conducting coating comprises silver.

16. A network in accordance with claim 11 in which said conducting coating comprises a mixture of silver powder, a synthetic resin, and an organic solvent for the resin.

17. A network in accordance with claim 11 in which said enamel comprises a suitable resinous material and a volatile solvent and said conducting coating comprises a mixture of silver powder, a synthetic resin, and an organic solvent for the resin.

18. A network in accordance with claim 11 in which said enamel comprises a suitable polymeric material and a, volatile solvent and said conducting coating comprises a mixture of silver powder, a synthetic resin, and an organic solvent for the resin.

19. A network in accordance with claim 11 in which said inductor comprises wire having an insulating covering.

20. A network in accordance with claim 11 in which said inductor comprises wire having an enamel coating.

TUDOR R. FINCH. DAVID A. McLEAN.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS 

